neoplasia-3.pdfdictionary if if I'd mix grid do

Functions of beta catenin
Beta catenin stimulates growth by two ways:
1. Inhibits contact inhibition by stimulating TWIST and SLUG
transcription regulators that decrease cadherin expression
2. Stimulates growth by increasing transcription of growth promoting
genes like cyclin D1 and MYC .
• APC suppresses growth by being part of a complex that destructs the
beta catenin.
• Beta catenin is an important component of WNT signaling
• WNT is a protein that induces cell proliferation by binding to a
receptor and transmit signals that prevent degradation of beta
catenin
• Undegraded beta catenin moves to the nucleus where it acts as a
transcription activator
recap
• In quiescent cells not exposed to WNT, cytoplasmic beta catenin is
degraded by destruction complex ( of which APC is a main
component)
• Loss of APC means that B catenin is not degraded and WNT pathway
activated even without the WNT
• This leads to transcription of growth promoting genes cyclin D1 ,MYC
and transcription regulators: TWIST AND SLUG that repress E cadherin
and thus reduce contact inhibition
Summary
• TGF beta- SMAD pathway is mutated in several cancers, mainly pancreatic and
colorectal. The pathway is the most well understood growth inhibition one and if
mutated, loss of growth inhibition occurs.
• Contact inhibition regulates cell growth. It is mainly mediated by E cadherin and
merlin.
• Tumors with lost E cadherin result in non-cohesive, usually single cell growth.
• APC gene is a tumor suppressor gene mutated in familial and sporadic colorectal
carcinoma.
• APC acts by being part of a destruction complex that destructs a growth
stimulator ( beta catenin).
• If the destruction complex is lost via deletions or deactivation mutations, Beta
catenin will be activated and translocated to the nucleus to stimulate other
transcription factors.inhibitors, continuation
• Normally growth inhibition is achieved by tumor suppressor genes. Loss or
decreased function of tumor suppressor genes allows cancer cells to
proliferate without being affected by inhibitory growth signals.
• Main genes/ pathways mutated to cause insensitivity to growth inhibition:
1. RB gene
2. TP53 gene
3. TGF beta pathway
4. Contact inhibition
5. APC gene
TGF beta pathway
• TGF beta ( transforming growth factor beta) is a potent inhibitor of
cell proliferation.
• TGF beta binds to receptors.
• Receptors activated .. Transmit signal through SMAD proteins to the
nucleus
• Transmitted signals to the nucleus result in transcriptional activation
of CDKIs and supression of MYC and CDK4.
• The result is growth inhibition.
TGF Beta
• TGF beta is a negative growth regulator.
• It binds to transmembrane receptors
• This binding stimulates second messengers in the
cytosol.. Of the SMAD family
• The message reaches the nucleus: to inhibit
growth through upregulation of CDKI and down
regulation of CDK4 and MYC.
• Mutations affecting TGF beta signaling causes cancer
• These mutations involve TGF b

1. Neoplasia 2023/2024
lecture 3
DrHeyamAwad
MD, FRCPath

2. ILOS
•1. List types of genes mutated or altered during carcinogenesis.
•2. Differentiate between oncogenes and tumor suppressor genes.
•3. Understand the mutational and non mutational genetic changes
responsible for carcinogenesis.

3. INTRO
•In this lecture we will start discussing how neoplasms, mainly
malignant ones, occur.
•As you know cancer is caused by mutations and DNA changes.. But
not any mutation will cause cancer.
•In this lecture we will take a broad look at the types of DNA changes
that can cause cancer and in the coming lectures we will discuss
specific mutations in detail.

4. Molecular basis of cancer
•Neoplasms are caused by nonlethal, genetic damage, which causes
uncontrolled cellular proliferation.
•Nonlethal: so cells can still multiply!
•Genetic damage: mutations or non-mutational damages (details later
in this lecture)
•Uncontrolled proliferation… not all genetic damages produce tumors,
they only do so if they result in a crazycell that can multiply
continuously in an uncontrolled, uninhibited fashion!

5. Tumor clonality
•Because tumor cells originate from one single genetically damaged
crazycell, they are clonal
•What does a clone mean?.. Refer to lecture 2!
•Note: tumors start as a clone, but with time they acquire several
mutations in some of the cells.. They become heterogeneous. This is
because some cells develop mutations that make them acquire
characteristics like: ability to invade, to metastasize.. etc

6. Tumor clonality
•So: malignant cells originate from one single transformed cell that
acquires a mutation allowing it to proliferate in an uncontrolled
manner.
•This cell keeps proliferating forming a clone.
•But the proliferating cells acquire additional mutations, that help the
tumor mass to grow further or to avoid death, or to metastasize ..etc.
•Each cell with a new mutation proliferates forming a sub-clone.
•The end result is a tumor mass where each cell has the original
mutation in the parent cell plus extra mutations that differ between
the sub-clones.

7. Carcinogenesis is a multistep process

8. What are the genetic damages that can
transform cells?
•For a genetic damage to transform a cell, it has to cause uncontrolled
proliferation.
•The majority of our cells proliferate continuously. This proliferation is
regulated by certain genes. There is a balance between genes that
stimulate growth and those inhibiting it. Loss of this balance can
cause uncontrolled proliferation.
•So : for cancer to occur there is stimulation of genes that cause cell
proliferation, or downregulation of genes that inhibit proliferation.

9. Cell cycle is regulated by a balance between growth stimulating genes =
protooncogenesand growth inhibiting genes= tumorsuppressor genes.

10. Proto-oncogenes normally stimulate growth in a
controlled manner. If they are mutated, they cause
uncontrolled growth ( cancer)

11. Tumor suppressor genes counteract the function of the oncogenes. If
they are inhibited by a mutation, then cells can proliferate without this
“braking” effect of the tumor suppressor genes.

13. Other genes involved in cancer
•Besides oncogenes and tumor suppressor genes, there are other types of
genes that are involved in transforming cells:
•-Genes that regulate apoptosis: these are very important because if the
damaged cell dies by apoptosis, then no proliferation is possible. So, these
genes are frequently mutated in cancers to keep cells alive and block
apoptotic messages.
•-DNA repair genes also play a role in carcinogenesis. If DNA damages are
repaired, then no cancer will occur. If DNA repair genes become
nonfunctioning, then there is a chance of DNA damages to accumulate in
cells.
•Genes that affect the interaction between tumourcells and host cells (
surrounding normal cells) also play a role in carcinogenesis.. Especially
genes which affect immune response of the host to cancer cells.

14. Genetic damages in neoplasms
So: five types of regulatory genes are mainly affected:
•1. growth promoting proto-oncogenes
•2. growth inhibiting tumor suppressor genes
•3. genes that regulate apoptosis
•4. genes involved in DNA repair.
•5.genes that regulate interactions between tumorcells and host
cells. Particularly important are genes that enhance or inhibit
recognition of tumorscells by the host immune system.

15. note
•Normal genes that cause cell proliferation are traditionally called:
proto-oncogenes.
•When they are mutated, they are called oncogenes.

16. oncogenes
•Normally: our cells have proto-oncogenes. These cause cell
proliferation in a regulated manner
•If the proto-oncogenes are mutated or overexpressed: they are called
oncogenes
•Proto-oncogenes encode for proteins: proto-oncoproteins, or
oncoproteins
•These oncoproteinsinclude: transcription factors, growth regulating
proteins, proteins involved in cell survival.

17. oncogenes
•Oncogenes cause overexpression of proteins involved in cell growth.
•If one allele is mutated or overexpressed: there will be increase in the
growth proteins, which is enough to increase cell growth
•So mutations of oncogenes act in a dominant manner .
•Important oncogenes : RAS and ABL

18. How oncogenes overexpressed??
•1. point mutation resulting in activation
•2. amplification : increased number of copies of the oncogenes
•3. translocations
•4.Epigenetic modification
•Details will follow . Don’t worry

19. Tumor suppressor genes
•They normally inhibit cell growth
•If mutated or lost: loss of growth inhibition : so tumors occur.
•Both alleles need to be lost or mutated for the tumors to develop….
Because if only one allele is lost , the other can compensate!
•So these arerecessive mutations ( two mutations in two alleles are
needed for cancer to occur)

20. Tumor suppressor genes
•Most important examples:
•1. RB gene(retinoblastoma gene) .. Called the Governor of the
genome: controls growth and puts a brake in cellular proliferation
•2. TP53 gene … guardian of the genome… it senses genetic damage.
So if there is damage it causes cessation of proliferation or if the
damage cannot be repaired it causes apoptosis.

21. Genetic lesions in cancer
•We now know the types of genes that should be damaged for cancer
to occur. But how they are damaged?
•They can be damaged by Mutational or non-mutational damages.
•Mutations: 1.subtle: point mutations, insertions, point deletions
:or 2. large, karyotypic change: translocations, large
deletions, gene amplification, aneuploidy
•Non mutational: MicroRNAs and epigenetic modifications

22. Genetic lesions in cancer

23. Point mutations
•These are single changes in nucleotides
•Point mutations that stimulate an oncogene or inhibit both alleles of a
tumor suppressor gene can result in cancer.

24. Balanced translocations
•Translocations can cause cancer if they increase expression of a proto-
oncogene.
•This can happen by two mechanisms:
•1. Removing the proto-oncogene from its normal, regulated locus to a
new position where it becomes under influence of a highly active
promoter.
•2. Translocation forms a new fusion gene that encodes a novel (new)
protein.

25. translocations
•In the upper example, the translocation created a new gene
ABL-BCR from fusion of two genes ( ABL and BCR). This
created a new tyrosine kinase that can activate cell
proliferation resulting in leukemia.
•In the other example in the picture, the translocation
moved the MYC oncogene to a new locus ( near the IG gene)
that increased expression of the MYC gene resulting in
increased cell proliferation

26. Philadelphia chromosome: an example of a translocation
causing a new protein ( a kinase) that increases cell
proliferation.

27. Translocations
•Occur mainly in haematogenousneoplasms ; why ??
•Because lymphoid cells make DNA breaks during antibody or T cell
receptor recombination. ( loads of cutting and rearrangements of the
genes… so there is more chance that a gene that was cut will be
“pasted “ in a new locus!

28. This table shows examples of tumors caused
by translocations. Don’t memorize it!!Tumor
type
translocationOncogene
affected
mechanism notes
BURKITT
lymphom
a
t(8;14) MYC MYC becomes
under
stimulation of
heavy chain
gene elements
90%of Burkittcases
have the mutation
overexpression
Follicular
B cell
lymphom
a
t(14,18) BCL2
(antiapoptotic)
Overexpression
of BCL2by
immunoglobulin
gene elements
overexpression
Chronic
myeloge
nous
leukemia
(CML)
t(9;22) BCR-ABL
rearrangement
New fusion
gene (
Philadelphia
chromosome)
90% of cases.
More details on next
slide!
Ewing
sarcoma
t(11;22) EWS –Fli1
fusion
Fusion gene EWS is a transcription
factor
Fusion product
Prostate
carcinom
a
ETS Fusion gene
Lung
cancer
ALK Fusion gene
causing
activation of
ALK kinase
Only 4% of lung
tumors havethis
fusion…these respond
to ALK kinase
inhibitors

29. Gene amplifications
•Proto-oncogenes can be amplified and overexpressed .. Converted to
oncogenes.
•This is seen in karyotyping as two patterns :1.homogenously stained
region (HSR) = increased copies of the gene present within the
chromosome
:2.Double minutes: extra copies of the gene separated
from the chromosome.

31. Deletions
•More in non-hematopoietic solid tumors
•Result in loss of tumor suppressor genes
•2 copies of the tumor suppressor gene need to be lost, usually one by
point mutation and another by deletion

32. Aneuploidy
•= abnormal number of chromosomes
•Result from errors of the mitotic checkpoint

33. microRNAs (miRNAs)
•Noncoding, micro RNA segments (22 nucleotides) that are negative
regulatorsof the genes.
•They inhibit gene expression post-transcriptionally= repress
translation or cleave mRNA.
•SO: transcription occurs = messenger RNA formed.. But mRNA is not
translated to a protein.
•microRNA can inhibit translation or cleave the messenger ( tears the
message before it is read)

34. miRNA
•Cause cancer by increasing oncogene expression or decreasing tumor
suppressor gene expression.

35. •miRNAsthat target oncogenes…. If reduced, then inhibition caused by
microRNA is lost causing overexpression of oncogenes.
•miRNAs that target tumor suppressor genes… if increased they cause
downregulation of tumor suppressor genes, resulting in cancer ( as if
we are functionally reducing the tumor suppressor genes)

36. miRNAs

38. epigenetics
•Epigenetics are reversible changes in gene expression that occur
without mutation.

39. Epigenetic mutations
•functionally relevant changes to the genome that do not involve a
change in the nucleotide sequence. Examples of mechanisms that
produce such changes are DNA methylation and histone modification,
each of which alters how genes are expressed without altering the
underlying DNA sequence.

40. Epigenetics and cancer
•Gene expression is silenced by DNA methylation= more methyl
groups lead to more silencing.
In cancer cells:
•1.Global DNA hypo methylation : increases expression of genes. Also
causes chromosomal instability
•2.Selective promoter hyper methylation of tumor suppressor genes:
silenced